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I'm not sure you and most other people can transact without fiat in countries where bitcoin or crypto is not legal as a means of payment. Fiat is needed in such cases - but bitcoin can still be used secretly, especially if you are willing to do so. But for the long term - I think bitcoin is the most recommended compared to gold or deposits.
You are right, bitcoin is not legal tender in countries that do not legalize it as a legal tender. If you visit my country, I will make sure you convert your bitcoin to fiat before you make any financial transactions or purchase anything. Bitcoin is legal as a commodity asset and can be traded and invested in, but it is not legal tender. I hope the regulations will change and become more bitcoin friendly in the future, but I don't think that will happen for a few years.
The price fluctuating due supply and demand all the time reflects that bitcoin will never be stable. Its volatility can be lower and it can be higher for some reason, but bitcoin price stability will never be achieved. Even if bitcoin is adopted as a global payment instrument and all countries have made it a strategic reserve, I still believe that its price fluctuation will never disappear and bitcoin will never be stable in price.